I want to share a misconception that caused Maven to fail when looking for artifacts. Im my example I was upgrading from Grails 1.2.0 to 1.2.1 and including a dependency to grails.org:grails-core:[1.2.1,1.2.1]. Maven would just complain with Couldn’t find a version in …, although I verified that this particular version is indeed available at the remote repository.

My misconception was, that when declaring a remote release repository <updatePolicy>never</updatePolicy> would only apply to existing artifacts, which – of course – need not be checked for remote changes (release artifacts must not change once they are released).

However, updatePolicy also applies to Maven meta data, i.e. which versions are available (and which one is the most current one). Thus, if there are any artifact versions already present in your local Maven repository, Maven will never download any version that is not yet present in your local repository 😦

See also Maven does not always download artifacts from specified repos.

With release repositories, the default value for updatePolicy is <updatePolicy>daily</updatePolicy>, which should be appropriate for most external Maven release repositories.

As we’re using a local Nexus for both hosting our own company repositories and for proxying external repositories as well, updatePolicy daily is too slow to avoid confusion when accessing internal releases from the Public Repositories group. So I chose to use <updatePolicy>always</updatePolicy> instead and let Nexus settings determine the interval at which it refreshes external repository artifacts:

<repository>
 <!-- Use our local Nexus Public Repositories Group -->
 <id>public</id>
 <name>Public Repositories</name>
 <url>http://ournexus.mycompany.com:8081/nexus/content/groups/public</url>
 <releases>
  <enabled>true</enabled>
  <updatePolicy>always</updatePolicy>
  </releases>
 <snapshots>
  <enabled>false</enabled>
 </snapshots>
</repository>